Studies in Lithium Oxide Systems: XI, Li2O–B2O3–P2O5

The glassforming region in the system was roughly outlined and liquidus data were obtained for the three joins LiPO₃-BPO₄, Li₄P₂O₇-BPO₄, and Li₃PO₄-Li₂B₄O₇. Compatibility relations for the ternary subsystems Li₄P₂O₇-BPO₄-P₂O₅ and Li₂O-Li₃PO₄-Li₂B₈O₁₃ were established. Two ternary compounds with the probable compositions 22Li₂O - 11B₂O₃ - 13P₂O₅ and 2Li₂O 3B₂O₃ P₂O₅ were detected.     

Phase Diagram for a Portion of the System Li2O-Nd2O3-P2O5

In the ternary system Li₂O-Nd₂O₃-P₂0₅, part of the phase diagram relevant to the growth of single LindP₄O₁₂ (LNP) crystals was examined. LNP melts incongruently and decomposes into NdP₃O₉ and liquid at the peritectic temperature of 970°C. For the crystal growth, an Li₂O-P₂O₅ mixture should be used as a flux. The melt compositions from which LNP nucleates were clarified.     

Strength and Microstructure in Lithium Disilicate Glass-Ceramics

The effect of heat treatment on the microstructure of Li₂O-Al₂O₃·SiO₂ glass-ceramics which contain crystals of either Li₂SiO₃, Li₂Si₂O₅, or both was investigated quantitatively. Strength determinations for abraded rods were correlated with heat treatment on the basis of both size and distribution of crystals and the type and amount of crystal phases present. The presence of Li₂Si₂O₅ crystals enhanced the strength, whereas the presence of Li₂SiO₃ crystals did not change the strength of the abraded parent glass. The interrelation between strength and microstructure is discussed.     

Crystallization Kinetics of a Complex Lithium Silicate Glass-Ceramic

Volume crystallization of this glass is nucleated by Li₃PO₄. On heating from room temperature, Li₂SiO₃ appears around 650°C and then converts to Li₂Si₂O₅ around 850°C by reaction with SiO₂ from the melt. Preheating the glass at 1000°C forms larger Li₃PO₄ nuclei that promote additional crystallization of cristobalite in the 650° to 850°C range. Crystallization activation energies calculated from scan-rate dependence of DTA peaks are 270 kJ/mol for Li₂SiO₃ and 360 to 570 kJ/mol for Li₂Si₂O₅.     

Studies in Lithium Oxide Systems: XII, Li2O-B2O3-Al2O3

Tentative phase relations in the binary system BnOa-A1₂O₃ are presented as a prerequisite to the understanding of the system Li₂O-B₂O₃-Al₂O₃. Two binary compounds, 2A1₂O₃.B₂O₃ and 9A1₂O₃.-2B₂O₃, melted incongruently at 1030° f 7°C and about 144°C, respectively. Two ternary compounds were isolated, 2Li₂O.A1₂O₃.B₂O₃ and 2Li₂O. 2AI₂O₃. 3B₂0₃. The 2:1:1 compound gave a melting reaction by differential thermal analysis at 870°± 20° C, but the exact nature of the melting behavior was not determined. The 2:2:-3 compound melted at 790°± 20° C to Li_zO.-5Al₂O₃ and liquid. X-ray diffraction data for the compounds are presented and compatibility triangles are shown.     

Studies in Lithium Oxide Systems: VII, Li2O–B2O2–SiO2

Phase relations in the system Li₂O–B₂O₃–SiO₂ were studied by quenching and solid-state reactions. No ternary compounds were detected in the portion of the system containing less than 53% Li₂O. Compatibility triangles were formed from the binary borate and silicate compounds. Liquidus data obtained by quenching are reported for four joins, Li₂O·2SiO₂–Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·B₂O₃, and Li₂O·2B₂O₃-SiO₂. The last join cuts across the two-liquid region and is not a true binary system. Some probable ternary invariant points were located in the portion of the system which was quenchable to glass and adjacent to the two-liquid region. Further data on the previously reported immiscible liquid formation are given and the significance is discussed. Data on the thermal expansion behavior of certain glasses are presented.     

Novel Fast Lithium Ion Conduction in Garnet-Type Li5La3M2O12 (M = Nb, Ta)

Lithium metal oxides with the nominal composition Li₅La₃M₂O₁₂ (M = Nb, Ta), possessing a garnetlike structure, have been investigated with regard to their electrical properties. These compounds form a new class of solid-state lithium ion conductors with a different crystal structure compared with all those known so far. The materials are prepared by solid-state reaction and characterized by powder XRD and ac impedance to determine their lithium ionic conductivity. Both the niobium and tantalum members exhibit the same order of magnitude of bulk conductivity (∼10⁻⁶ S/cm at 25°C). The activation energies for ionic conductivity (<300°C) are 0.43 and 0.56 eV for Li₅La₃Nb₂O₁₂ and Li₅La₃Ta₂O₁₂, respectively, which are comparable to those of other solid lithium conductors, such as Lisicon, Li₁₄ZnGe₄O₁₆. Among the investigated materials, the tantalum compound Li₅La₃Ta₂O₁₂ is stable against reaction with molten lithium. Further tailoring of the compositions by appropriate chemical substitutions and improved synthesizing methods, especially with regard to minimizing grain-boundary resistance, are important issues in view of the potential use of the new class of compounds as electrolytes in practical lithium ion batteries.     

Studies in Lithium Oxide Systems: V, Li2O-Li20 B2O3

Nine compositions containing 40 to 68% B₂O₃ were used to study the high-lithia portion of the system Li₂O-B₂O₃ by quenching and differential thermal analysis methods. The compounds 3Li₂O 2B₂O₃ and 3Li₂O B₂O₃ melted incongruently at 700°± 6°C, and 715°± 15°C., respectively. The compound 2Li₂O B₂O₃ is assumed to dissociate slightly below 650°± 15° C., although the data could also be interpreted as in-congruent melting. Below 600°± 6°C. it does dissociate to the 3:2 and 3:1 compounds. In this narrow temperature interval the 2:1 compound had an inversion at 618°± 6°C. Both forms of the 2:1 compound could be quenched to room temperature. X-ray diffraction data for the compounds are tabulated, and the complete phase diagram for the system Li₂O-B₂O₃ is presented.     

Glass Transition and Infrared Spectra of Low-Alkali, Anhydrous Lithium Phosphate Glasses

Anhydrous glasses in the series x Li₂O + (1 - x )P₂O₅ have been prepared and characterized in the range 0 ≤ x ≤ 0.5. FT-IR spectroscopy and glass transition temperature measurements have been used to explore the structure and a key physical property of the low-alkali phosphate glasses. The structure of v -P₂O₅ is proposed to consist of a 3-D network of trigonally connected tetrahedra decorated with a P=O unit. Contrary to what has long been proposed for these glasses, the addition of alkali degrades the 3-D network through the generation of nonbridging oxygens rather than strengthen the network through the proposed alkali ion bridging. The T _g of v -P₂O₅ is ∼653 K and decreases some 130 K with the addition of 10 mol% Li₂O. T _g then reaches a minimum value at 20 mol% Li₂O and increases with further Li₂O additions. The increase in T _g, even though the fraction of nonbridging oxygens is still increasing, is interpreted in terms of an increasing entanglement of long-chain PO₂ groups in the glass. Such a structural transition from a 3-D network of interconnected PO₄ groups for P₂O₅ to a 1-D chain structure for LiPO₃ is one of the first examples of the importance of intermediate-range order in governing the properties of glass.     

The System SiO2–P2O2

Phase relations in the binary system between SiO₂-P₂O₅ and SiO₂ were investigated by the quenching method using sealed platinum tubes to prevent the loss of P₂O₅. The compound Si0₂-P₂O₅ exists in two forms, the low-temperature β form inverting sluggishly but reversibly to the high-temperature β form at 1030°C. The β form melts congruently at 1290°C. The compound 2SiO₂-P₂O₅ melts incongruently at 1120°C to a silica-rich liquid and SiO_a-P₂O₅. In the region between 5 and 25 mole % PO₂, reactions were so sluggish that no data could be obtained by quenching.     

The System ThO2-P2O5

The existence of compounds with 1:1, 3:2, and 3:1 ThO₂:P₂O₅ ratios in the system ThO₂-P₂O₅ was confirmed. A 1:2 compound found by previous workers was not investigated, and their 2:1 compound was not detected; however, extensive solid solution on either side of the 3:2 compound was established. The linear thermal expansion behavior of the compounds and solid solutions was determined.     

Studies in Lithium Oxide Systems: IX, Li2o-Al2O3-TiO2

Compatible phases in the system Li₂O-Al₂O₃-TiO₂ at various temperature levels were determined mainly by solid-state reactions for the portion of the ternary system bounded by Li₂O Al₂O₂, Li₂O.TiO₂, Al₂O, and TiO₂. The existence of a ternary compound, Li₂O.Al₂O₃.4TiO₂, and nine joins was established. The ternary compound has a lower limit of stability at 1090°± 15°C. and dissociates and recombines rapidly at 1380°± 15°C.     

Sol–Gel Preparation and Characterization of Lithium Disilicate Glass–Ceramic

A sol–gel process is described for preparation of crystalline lithium disilicate (Li₂Si₂O₅) from tetraethylorthosilicate and lithium ethoxide. The glass network structure and crystallinity resulting from heat treatment at temperatures from 150° to 900°C were investigated by nuclear magnetic resonance, X-ray diffraction, and differential scanning calorimetry/thermogravimetric analysis. Q³ structural units (SiO₄ tetrahedra with three bridging oxygen atoms) formed in the amorphous gel at a low temperature (≤150°C) persist to elevated temperature (≤500°C) and directly transform to crystalline Li₂Si₂O₅ at about 550°C. The heating schedule slightly affects the crystalline phase transformation.     

Partial Bi-Sr-Cu-O Subsolidus Diagram at 800°C with and without Lithium Carbonate

Solid-phase relationships have been determined for the Bi₂O₃–SrO–CuO system at 800°C in air with and without Li₂CO₃ mineralizer. Two ternary compounds were detected with Bi:Sr:Cu ratios of approximately 2:2:1 and a solid-solution phase 11−;x:9+x:5 with 0x0.4. The solid-solution phase is a 9 K super-conductor at x=0.4. Two additional compounds with Bi:Sr:Cu ratios of approximately 4:9:1 and 2:7:2 are apparently stabilized by the presence of Li₂CO₃, but do not form without it. X-ray crystallographic data are provided for each compound. Ramifications for quaternary Bi:Sr:Ca:Cu-O superconductors are discussed.     

Reactions in the System TiO2-P2O5

The system TiO₂-P₂O₅ was investigated in the compositional range TiO₂.P₂O₅ to 100% TiO₂. Two compounds exist, TiO₂.P₂O₅ and 5TiO₂.-2P₂O₅. TiO₂.P₂O₅ begins to lose P₂O₅ at 1400°C. and both fusion and vaporization proceed rapidly at 1500°C. 5TiO₂.2P₂O₆ melts congruently at 1260°± 3°C. to a glass which can be retained in substantial quantities at room temperature. Physical properties of certain compositions are described.     

Mineralizing Effect of Li2B4O7 and Na2B4O7 on Magnesium Aluminate Spinel Formation

Lithium borate (Li₂B₄O₇) and sodium borate (Na₂B₄O₇) mineralize spinel formation from stoichiometric MgO and Al₂O₃ between 1000° and 1100°C. Mineralization with both compounds is shown to be mediated by B-containing liquids which form glass on cooling. However, the liquid compositions depend on the type of mineralizer and temperature, suggesting that templated grain growth or dissolution–precipitation mechanisms are operating, one dominating over the other under certain conditions. Na₂B₄O₇-mineralized compositions show predominantly templated grain growth at 1000°C, which changes to dissolution–precipitation at 1100°C, whereas Li₂B₄O₇-mineralized compositions show dissolution–precipitation from 1000°C. Li₂B₄O₇ is a stronger mineralizer as spinel formation is complete with 3 wt% Li₂B₄O₇ at 1000°C and with ≥1.5 wt% addition at 1100°C, whereas Na₂B₄O₇-mineralized compositions are found to retain some unreacted corundum even at 1100°C.     

Studies in Lithium Oxide Systems: II, Li2O Al2O3–Al2 O 3

Solid-state reactions between Li₂O and Al₂ O₃ were studied in the region between Li₂O.Al₂ O ₃ and Al₂ O ₃. The compound Li₂ O Al₂ O ₃ melts at 1610°± 15°C. and undergoes a rapid reversible inversion between 1200° and 1300°C. Vaporization of Li₂ O from compositions in the system proceeds at an appreciable rate at 1400°C, as shown by fluorescence. Lithium spinel, Li₂ O -5Al₂O₃, was the only other compound observed. The effect of Li₂ O on the sintering of alumina was investigated.     

Phase Equilibria in the System Na2SiO3-Li2SiO3-SiO2

Ternary phase relations have been studied and several modifications made to Kracek's phase equilibrium diagram. These include location of the primary phase fields of Na₆Si₈O₁₉ and Li₂Si₂O₅. Metastable phases and polymorphs were often encountered, notably a primary phase, δ-Na₂Si₂O₅, and a new polymorph of Li₂Si₂O₅.     

Solid State Reactivity and Glass Crystallization Behavior of Some Alkali Aluminogermanates

A preliminary examination of the crystallization sequences in some alkali aluminogermanate glasses is described. The glasses investigated are represented by the following chemical formulas: [Li₃AlGeO₄], [LiAlGe₂O₆], [NaAl-GeO₄], [Li₃AlGe₃O₉], [Li₂NaAlGe₃O⁹], and [Li₂-KAlGe₃O₉]. Three new compounds, KAlGeO₄, RbAlGeO₄, and CsAlGeO₄, were synthesized in the solid state. A simple, arithmetical approach is presented for determining the statistical existence of six-coordinated germanium (IV) in a given glass. The experimental results, particularly in [LiAlGeO₄], [LiAlGe₂O₆], and [Li₃AlGe₃O₉], indicate that the potential existence of six-coordinated germanium (IV) has a substantial effect on the mechanism as well as on the energetics of the respective glass crystallizations.     

Phase Equilibria in the System Li2O-CaO-SiO2

Phase relations in the system Li₂O-CaO-SiO₂ were studied by the quenching method. Four stable ternary compounds were found (Li₂Ca₃Si₆O_l6, Li₂Ca₄Si₄O₁₃, Li₂Ca₂Si₂O₇, and Li₂CaSiO₄) as well as phase Y , which is probably a metastable orthosilicate fairly close to Ca₂SiO₄ in composition. X-ray powder data are given for the new phases. Eleven subsolidus compatibility triangles and thirteen liquidus invariant points were located. Melting relations were determined for that part of the system bounded by Li₂SiO₃, Li₂CaSiO₄, Ca₂SiO₄, and SiO₂. The join Li₂SiO₃-CaSiO₃ is binary.